Bridge igniter

ABSTRACT

The present invention relates to a bridge igniter  1  having: a resistance layer  3  which has a given electrical resistance and which can be heated by an electrical current; an electrical insulating layer  4  that is disposed on the resistance layer  3  and has a given thermal conductivity; a reactive layer that is disposed on the insulating layer, the insulating layer  4  transmitting the heat that is produced in the resistance layer  3  to the reactive layer  5,  thereby causing the latter to undergo an exothermic reaction; and a pyrotechnic layer  7  that is disposed on or above the reactive layer  5  and that may be set off by the exothermic reaction of the reactive layer  5.

BACKGROUND INFORMATION

[0001] The present invention relates to a bridge igniter, especially a reactive bridge igniter.

[0002] Although applicable to any bridge igniter, the present invention and the set of problems on which it is based are explained in relation to a bridge igniter for triggering airbags and seat-belt tighteners in motor vehicles.

[0003] Bridge igniters that are made up of a resistance layer and a reactive layer disposed on top of it, the resistance layer being heated using an electric current, are known to the applicant. The reactive layer, also heated, reacts exothermically and initiates a pyrotechnic material lying on top of it.

[0004] The fact that the electrical resistance of the bridge igniter or of the resistance layer cannot be adjusted independently of the material of the reactive layer or its thickness, because these two layers are in electrical contact with each other, has proven to be disadvantageous in the known approach described above. Thus, a greater energy input is required to generate the Joule-effect heat necessary to fire the reactive bridge igniter.

[0005] Moreover, under certain circumstances, several adhesive layers are necessary between the resistance layer and the reactive layer for an improved mechanical adhesion, which also increase the process costs.

[0006] Thus, the object of the invention is generally to create bridge igniters of this type which minimize the energy input necessary to fire the pyrotechnic material and at the same time allow the ignition bridge resistance to be adjusted over a greater range, independent of the thickness of the reactive layer.

ADVANTAGES OF THE INVENTION

[0007] The idea on which the present invention is based is that the bridg igniter has: a resistance layer which has a given electrical resistance and which can be heated by an electrical current; an electrically insulating layer that is disposed on the resistance layer and has a given thermal conductivity; a reactive layer that is disposed on the insulating layer, the insulating layer transmitting the heat that is produced in the resistance layer to the reactive layer, thereby causing the latter to undergo an exothermic reaction; and a pyrotechnic layer that is disposed on or above the reactive layer and may be set off by the exothermic reaction of the reactive layer.

[0008] The bridge igniter of the present invention having the features of claim 1 has the advantage over the known approach that the resistance of the bridge is adjustable over a greater range and is independent of the reactive layer material and its thickness. Thus, the electrical resistance of the resistance layer is the sole factor determining the energy input required to fire the bridge igniter. The electrical separation of resistance layer and reactive layer by the insulating layer allows the electrical resistance of the resistance layer to be adjusted independently of the material characteristics and thickness of the reactive layer.

[0009] Moreover, the insulating layer may simultaneously function as an adhesive layer between the resistance layer and the reactive layer. Additional production steps for forming such an adhesive layer are eliminated.

[0010] Moreover, the insulating layer may be used as a diffusion barrier between the resistance layer and the reactive layer, a diffusion of atoms and/or ions of the reactive layer material into the resistance material, for example, thereby being prevented.

[0011] Advantageous developments and improvements of the bridge igniter indicated in claim 1 are found in the dependent claims.

[0012] According to a preferred development, the insulating layer is formed as an oxide layer, especially as a copper oxide or silicon dioxide layer. These layers, which have a given thickness, simultaneously ensure a good electrical insulation and a thermal connection between the resistance layer and the reactive layer.

[0013] According to another preferred development, the insulating layer has a thickness of approximately 50 to 100 nm. Such thicknesses must be adapted to the corresponding materials in such a manner that they fulfill the given characteristics.

[0014] According to another preferred development, the resistance layer is specifically made of palladium or nickel-chromium.

[0015] According to another preferred development, the reactive layer is specifically made of zirconium or hafnium.

[0016] According to another preferred development, the resistance layer has an adhesive layer, for example a titanium layer, disposed on it. This adhesive layer provides a better mechanical adhesion of the reactive layer or the insulating layer on the resistance layer. Most favorably, the insulating layer itself may function as an adhesive layer between the resistance layer and the reactive layer. Consequently, the step of manufacturing an additional adhesive layer may be omitted.

[0017] According to another preferred development, a co-reactant cooperates with the reactive layer to produce an exothermic reaction in it. As a result, an additional amount of heat is released which may be necessary to set off the pyrotechnic material.

[0018] According to another preferred development, the insulating layer functions as a co-reactant. The reactive layer reacts exothermically when it cooperates with an oxide layer, for example. Thus, no additional co-reactants have to be produced.

[0019] According to another preferred development, the reactive layer has a co-reactant, specifically an oxide layer, disposed on it. This co-reactant is also used to initiate an exothermic reaction in the reactive layer.

[0020] Another preferred development provides a plurality of reactive layers and co-reactants in alternating sequence to produce a multi-layer structure, the co-reactants being formed in particular as oxide layers of the material of the corresponding reactive layers. This results in a sandwich-type structure, which contributes to improving the course of the reaction by enlarging the reaction surface.

[0021] According to another preferred development, the insulating layer functions as a diffusion barrier between the resistance layer and the reactive layer.

[0022] According to another preferred development, electrical contact surfaces, for example, gold plates, are connected to the resistance layer in order to supply electricity to it. The size, shape and material of the contact surfaces are adapted to the desired electrical energy to be supplied.

[0023] According to another preferred development, the bridge igniter is disposed on a substrate, for example, a silicon substrate, a ceramic, a plastic or an integrated circuit (IC). When the bridge igniter is disposed on an integrated circuit, the contact surfaces are not necessary, because the resistance layer may be supplied with electrical energy via supply leads of the integrated circuit. Thus, the overall structure is simplified and a more compact component is produced.

[0024] According to another preferred development, the resistance layer is configured in the shape of a bridge. As a result, the resistance of the resistance layer may be increased and more Joule-effect heat may be generated.

DRAWING

[0025] Exemplary embodiments of the invention are illustrated in the drawing and explained in detail in the following description.

[0026] The figures show:

[0027]FIG. 1A top view of a resistance layer of a bridge igniter according to a first exemplary embodiment of the present invention;

[0028]FIG. 2A top view of a bridge igniter according to the first exemplary embodiment of the present invention;

[0029]FIG. 3A cross-sectional view of the bridge igniter in FIG. 2 according to the first exemplary embodiment of the present invention; and

[0030]FIG. 4A cross-sectional view of a bridge igniter according to a second exemplary embodiment of the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0031] In the figures, the same reference numbers designate the same or functionally equivalent components.

[0032]FIG. 1 illustrates a top view of a resistance layer 3 of a bridge igniter 1 according to a first exemplary embodiment of the present invention.

[0033] Resistance layer 3 is configured with an “H” shape and has a central bridge that connects two rectangular-shaped areas 31 to each other. It is advantageously made of palladium or nickel chromium. Palladium has a relatively poor adhesion characteristic, so that an adhesion layer 9 is advantageously disposed on resistance layer 3 for a better mechanical adhesion of insulating layer 4 or reactive layer 5 to the resistance layer.

[0034] Bridge 30 has a thickness of approximately 100 nm to 150 nm and width or length dimensions of approximately 30 μm to 60 μm.

[0035]FIGS. 2 and 3 show, respectively, a top view and a cross-sectional view of a bridge igniter 1 according to the first exemplary embodiment of the present invention.

[0036] Contact surfaces 10, advantageously gold contact surfaces, are applied to areas 31 of resistance layer 3 to supply electrical energy. Contact surfaces 10 advantageously have dimensions of approximately 300 μm to 500 μm.

[0037] An insulating layer 4, advantageously an oxide layer 4, is disposed on bridge 30 of resistance layer 3. Insulating layer 4 is advantageously formed as a copper oxide or silicon dioxide layer and has a thickness of approximately 50-100 nm. Obviously, other insulating materials may also be used. What is decisive is just that the dimensions and the material of insulating layer 4 are selected so as to ensure, on the one hand, good electrical insulation between resistance layer 3 and reactive layer 5, and on the other hand, a good thermal connection between these two layers.

[0038] Insulating layer 4 also functions as a diffusion barrier between resistance layer 3 and reactive layer 5. Atoms or ions are thus unable to migrate from one layer into the other and unfavorably change the material characteristics.

[0039] As is evident in FIG. 3, a reactive layer 5 that is made of zirconium or hafnium, for example, and has a thickness of approximately 500 nm to 1 μm is arranged on insulating layer 4. The reactive layer 5 selected for this must not be too thin, so that there may be a sufficiently high input of energy.

[0040] The arrangement described above may be located on a substrate 2, as is evident in FIG. 3. Substrate 2 is advantageously formed as a silicon substrate, silicon dioxide substrate, ceramic, plastic (polyimide film) or as an integrated circuit. Substrate 2 has an approximate thickness of 100 μm to 500 μm, depending on its material, even greater thicknesses, such as with plastic, being advantageous.

[0041] It is also advantageous to provide an adhesive layer 9 between substrate 2 and the resistance layer for better mechanical adhesion.

[0042] When bridge igniter 1 is disposed on an integrated circuit 2, it is possible to supply electrical energy to resistance layer 3 via electrical leads of the integrated circuit. This means that contact areas 10 are no longer necessary.

[0043] As is evident in FIG. 3, the electrical energy is advantageously supplied via contact areas 10 on resistance layer 3 using a charged capacitor. Because of the electrical resistance of resistance layer 3, the flow of electrical current produces heat due to the Joule-effect, and the resistance layer heats to a specified temperature, which, depending on the material, may be several thousand degrees Celsius.

[0044] Insulating layer 4 electrically separates reactive layer 5 from resistance layer 3 in such a manner that reactive layer 5 does not contribute to the total electrical resistance. Nevertheless, insulating layer 4 conveys the Joule-effect heat that is generated in resistance layer 3 to reactive layer 5, producing an exothermic reaction in the latter.

[0045] As is recognizable in FIG. 3, reactive layer 5 advantageously has a co-reactant 6 on it that initiates the exothermic reaction in reactive layer 5. Co-reactant 6 is advantageously made of copper oxide or manganese oxide and has a thickness of approximately 1 μm to 2 μm.

[0046] A pyrotechnic material (not shown), which may be set off by the exothermic reaction of reactive layer 5 with co-reactant 6, is provided on or above co-reactant 6.

[0047]FIG. 4 illustrates a cross-section of a bridge igniter according to a second exemplary embodiment of the present invention.

[0048] In contrast to the first exemplary embodiment shown in FIGS. 2 and 3, co-reactant 6 has a second reactive layer 50 on it. Second reactive layer 50 in turn has a corresponding second co-reactant 60 on it. This sequence of reactive layers and corresponding co-reactants may be continued as much as desired.

[0049] This multi-layer structure enlarges the reaction surface, that is the interface of reactive layers 5, 50 with corresponding co-reactants 6, 60, and increases the reaction speed.

[0050] Co-reactants 6, 60 are advantageously produced from the same material as insulating layer 4, especially as oxide layers of the material of corresponding reactive layers 5, 50.

[0051] The pyrotechnic material is, for example, zirconium-potassium perchlorate (ZPP), which has an ignition temperature of approximately 400° C.

[0052] Sample numbers are given below to give a feeling for the corresponding orders of magnitude. Due, for example, to the discharge of a capacitor, a current intensity of approximately 5 amps flows for a period of about 10 μs through resistance layer 3 having an electrical resistance of several ohms, a temperature of up to 3000° C. being produced via bridge 30 of resistance layer 3.

[0053] Although the present invention was described above in terms of preferred exemplary embodiments, it is not limited to them, but rather is modifiable in numerous ways.

[0054] In particular, insulating layers 4 may also be formed as oxide layers of the reactive material and/or of the resistance material.

[0055] Furthermore, the multi-layer structure represented in FIG. 4 may be expanded as much as desired. 

What is claimed is:
 1. A bridge igniter (1) comprising: a resistance layer (3) having a given electrical resistance which can be heated by an electrical current; an electrical insulating layer (4) that is disposed on the resistance layer (3) and has a given thermal conductivity; a reactive layer (5) that is disposed on the insulating layer, the insulating layer (4) transmitting the heat generated in the resistance layer (3) to the reactive layer (5), thereby causing the latter to undergo an exothermic reaction; and a pyrotechnic layer (7) that is disposed on or above the reactive layer (5) and may be initiated by the exothermic reaction of the reactive layer (5).
 2. The bridge igniter as recited in claim 1, wherein the insulating layer (4) is formed as an oxide layer, especially as a copper oxide or silicon dioxide layer.
 3. The bridge igniter as recited in one of claims 1 or 2, wherein the insulating layer (4) has a thickness of approximately 50 nm to 100 nm.
 4. The bridge igniter as recited in one of the preceding claims, wherein the resistance layer (3) is formed in particular of palladium or nickel-chromium.
 5. The bridge igniter as recited in one of the preceding claims, wherein the reactive layer (5) is formed in particular of zirconium or hafnium.
 6. The bridge igniter as recited in one of the preceding claims, wherein an adhesive layer (9), such as a titanium layer, is disposed on and/or under the resistance layer (3).
 7. The bridge igniter as recited in one of the preceding claims, wherein the insulating layer (4) functions as an adhesive layer (9) between the resistance layer (3) and the reactive layer (5).
 8. The bridge igniter as recited in one of the preceding claims, wherein a co-reactant (6) cooperates with the reactive layer (5) to produce an exothermic reaction in the latter.
 9. The bridge igniter as recited in claim 8, wherein the insulating layer (4) functions as a co-reactant (6).
 10. The bridge igniter as recited in one of the preceding claims, wherein a co-reactant (6), especially an oxide layer, is disposed on the reactive layer (5).
 11. The bridge igniter as recited in claim 10, wherein a plurality of reactive layers (5; 50) and co-reactants (6; 60) are provided in alternating sequence to produce a multi-layer structure, the co-reactants (6; 60) being formed in particular as oxide layers of the material of the corresponding reactive layers (5; 50).
 12. The bridge igniter as recited in one of the preceding claims, wherein the insulating layer (4) functions as a diffusion barrier between the resistance layer (3) and the reactive layer (5).
 13. The bridge igniter as recited in one of the preceding claims, wherein electrical contact surfaces (10), gold plates for example, are connected to the resistance layer (3) in order to provide it with electrical power.
 14. The bridge igniter as recited in one of the preceding claims, wherein the bridge igniter (1) is disposed on a substrate (2), for example, a silicon or silicon dioxide substrate, a ceramic, a plastic or an integrated circuit.
 15. The bridge igniter as recited in claim 14, wherein the integrated circuit supplies electrical energy to the resistance layer (3).
 16. A process as recited in one of the preceding claims, wherein the resistance layer (3) is configured in a bridge shape. 